Hunterston B, which employs 700 people, had been scheduled for shut-down in 2011, but this was previously extended to 2016.

The Scottish Government is firmly opposed to the construction of a new generation of nuclear power stations, but welcomed the move yesterday, insisting it is “perfectly open” to the continued operation of Hunterston and its younger sister station at Torness in East Lothian.

The welcome given to this decision by the Scottish Government leaves the SNP’s supposed anti-nuclear policy mired in confusion

He said last night: “The welcome given to this decision by the Scottish Government leaves the SNP’s supposed anti-nuclear policy mired in confusion. Where SNP spokespeople claim opposition to nuclear power, Alex Salmond and his ministers in Edinburgh now say they support the lifetime extension of Hunterston.

“People in Scotland will rightly wonder whether the SNP will say and do anything to get votes in the run up to the referendum.

“In a separate Scotland, without new nuclear, we would become reliant on importing nuclear-generated energy from abroad on a commercial basis, rather than as part of a unified energy market as at present.”

The operating extension of the plant, which generates enough electricity to supply almost half of ­Scotland’s homes, was announced by EDF Energy chief executive Vincent de Rivaz.

Station director Colin Weir said: “I am delighted that it gives my staff many more years of job security, and for the positive effect that that in turn has on the local economy.”

EDF Energy estimated the financial benefits to the local economy at £40million a year. Torness nuclear power station near Dunbar, East Lothian, which is also owned by EDF, is also due to close in 2023.

A Scottish Government spokesman said: “We have consistently made it clear that nuclear energy will be phased out in Scotland over time, with no new nuclear build taking place in Scotland.

“But we have also consistently made clear that this does not preclude extending the operating life of Scotland’s existing nuclear stations to help maintain security of supply over the next decade while the transition to renewables and cleaner thermal generation takes place.”